/*
 * @lc app=leetcode.cn id=6 lang=java
 *
 * [6] Z 字形变换
 */

// @lc code=start
class Solution {
    public String convert(String s, int numRows) {
        if(numRows<2){
            return s;
        }
        List<StringBuilder> rows=new ArrayList<StringBuilder>();
        for (int i = 0; i < numRows; i++) {
            rows.add(new StringBuilder());
        }

        int i=0,flag=-1;
        for(char c:s.toCharArray()){
            rows.get(i).append(c);
            if(i==0 || i==numRows-1){
                flag=-flag;
            }
            i+=flag;
        }
        StringBuilder sb=new StringBuilder();
        for (StringBuilder row:rows) {
            sb.append(row);
        }
        return sb.toString();
    }
}
// @lc code=end

